Private automatic exchange line adapter for mobile radio system



L. G. ECKMANN ETAL PRIVATE AUTOMATIC EXCHANGE LINE ADAPTER FOR MOBILE RADIO SYSTEM Filed Aug. 28, 1952 Jan. 17, 1956 ATTY.

nited States Patent' PRIVATE AUTOMATIC EXCHANGE LINE ADAPTER FOR MOBILE RADIO SYSTEM Application August 28, 1952, Serial No. 306,816

Claims. (Cl. 250- 6) The present invention'relates to the communication arts in general, and more particularly to aradio telephone system comprising a number of private, automatic exchange stations and a number of mobile units whereby the subscribers located thereat, through the medium of .a central station possessing the main transmitter and receiver, may establish contact with each other and converse with each other over the facilities furnished by said linking central station.

The principal object of the invention is to provide a radio telephone system which makes it possible for a private automatic exchange subscriber to communicate through a link station, equipped with special facilities, with a mobile station over a single pair of radio frequency channels serving all the mobile stations, one of the chan` nels being used for transmitting and the other channel.

anice cation taken in connection with the accompanying drawmg.

The drawing is subdivided by broken lines Linto three sections representing the private automatic exchange, P. A. X 100, the attendant station 200, and the radio terminal 300, together with radio mobile stations 400-402. The radio terminal 300 may be located at or near the attendant station 200, or it may be situated at some remote position which is most advantageous for radio wave transmission and reception and connected by a line with the attendant station 200.

The private automatic exchange shown in simplified manner as P. A. X 100 consists of a connector 101 which will' connect incoming calls from a plurality of exchange subscribers over the lines 104 and 105 through the connector 101 to the P. A. X line comprising conductors 106 and 107, which lead into the attendant station 200. Outgoing calls from the attendant station 200 go over conductors 108 and 109 through the line circuit 103 and then through a rotary line switch, not shown, and a iinal switch such as the connector switch 102, to theA line of the called subscriber station. Whenever a call comes in (P. A. X) station subscriber by way of the link or attendant station having an operator thereat to supervise the calls.

A more detailed object of the invention concerns itselii with the methods used for signalling theoperator at the link station to indicate an incoming call whether from a P. A. X subscriber or a radio mobile subscriber.

Another object concerns itself with methods employed for monitoring, at the will of the station operator, any conversation between the various subscribers and also means whereby the operator can converse privately with either a P. A. X station subscriber or the mobile subscribers. i I v Another object deals with a circuit which is controlled by the P.V A. X subscriber to automatically shut cti the station transmitter and signal-the operator when the call has been terminated, the control'being exercised by replacing the handset.

A further object is to provide a circuit arrangement together with associated components which are activated upon receipt of a carrier wave transmitted by a transmitter from any calling mobile station, which carrier wave automatically turns on the station transmitter to rebroadcast the calling mobiley subscribers signal to the called subscribers mobile station. Y

Another object is to provide means controlled by the operator to lock the station transmitter on the air during a call between two mobile station subscribers and to busy the P. A. X line connecting the private automatic exchange to the attendantstation to advise a 'calling P. A. X subscriber that the P. A. X-to-mobile subscriber I inkis not at that .time available to him.

The invention, both as to its organization and method of operation together with further objects and advantages thereof, Will best be understoodby reference tothe speciiifrom the P. A.' X 100 into the attendant station 200, two methods are used for signalling the operator thereat, namely the P. A. X supervisory lamp 214 and the buzzer 227.. In response to the call the operator at the attendantstation 200 operates the ANS Key 220 to the P. A. X position. This closes the contacts 226 which complete an operating circuit to relay 240 thereby opening the circuit to buzzer 227 when contacts 242 open up and connects the operator telephone circuit 230 to the P. A. X line by closure of contacts 223 and 224. The P. A. X supervisory lamp 214 remains lit for the duration of the call. The ANS Key 220 is also used for connecting the operator to the radio trunk 237 and 23S whenever an incoming call originates at any one of the radio mobile stations. Monitor speaker 201 is additional equipment which can be used if desired. Switch 203 connects ther monitor amplifier 202 to the operator telephone circuit 230. The Monitor-RLS Key 231 as shown on the drawing is in the normal position. This is a three-position key in which the MON position is a locking position and the RLS position is a non-locking position. When the key is put to MON position, contacts 232, 234 and 235 will be closed. Contacts 236 will continue to be closed. When the switch is momentarily put in the RLS position, the only contactsv that will open up will be 236, contacts 232, 234 and 235 continuing toremain open. The purpose of the Trunk Key 264, a non-locking key, is to energize relay 250 which will close the circuit between the P. A. X line 106 and 107 and the radio trunk 237 and 238. Contacts 255 on relay 250 are used to eect a permanent ground for the simplex leg of the radio trunk 234 and 28S so as to lock permanently the radio transmitter 330 on air when relay 360 locks because of the effected ground. The Radio supervisory lamp 283 is used to signal the operator at the attendant station 200 of an incorning call from any one of the radio mobile stations. This light remains illuminated during the period of the initiated call.- Dividing networl`310 is used to connect the radio receiverv 340 and the transmitter 330 to the radio trunk 237 and 238. The repeating coils 265 and 301 furnish a simplex control circuit for the transmitter 330.

A call may be initiated by a P. A. X subscriber station over the lines 104 and 105 through the P. A. X over the line 106 and 107 which signals the operator at the attendant station 200 by means of the P. A. X supervisory lamp 214 and the buzzer 227. The operator moves the ANS Key 220 to the P. .-A. X position and receives the calling subscribers instructions. 'After determining what radio mobile station the calling subscriber is desirous of contacting, the operator moves 3 tleANS Key 220 toY thek Radio position thereby ener.- gizi-ng relay- 260l whenY contactsl 221' clor Relay' 280- operates because of the ground connection made at the make contacts 261 of relay 260. This also results in operation of relay" 361!A which turns on the' radib' transmitter 330. The operator. then speaks into the handset located'at the operators' telephone circuit; 230 and' calls the, desired radio mobile. unit. When the called sub; scriber at the radio mobile, unit'. responds, the. operator operates momentarily the Trunk Key. 264 which energizes relay 250 thereby connectingl the;call ingsub$criber on the line 106' and'10 7 to the radio trunkv 237 and 2,38.

Thereafter the operator` di'scot 1nectsV the operator telef phone circuit 23Bifrom the radio trunk` 2.37, and` 233 by operating the ANS Key 2 270 to the, normal. position. After the,- conversation has beenterminated andthe calling subscriber Hangs.' uprthebattety is reversed." 0n. line 106i and' 10.7'V in. a manner to lie-hereinafter exrlained. which Vcauses reay 21.0 to release because oi ythe inability of the reversed; Current to. ow backward through the, rectier 208,.' Relay 2.5.0V releases and opens a circuit to relay Slwlii'chin turn shuts. down the radiol trans: mitter 330- Whenever a subscriber at the mobile station wants. to make a call toa P. A.. XQ subscribers. the.. mobile station subscriber turnsn on the' radio. transmitter located at the mobile station which transmits, a carrier.k wave. signalv whichv is picked' up by the radio receiver 3.210

located atY the radio terminal 3,08 and connected to the.

attendant station 2%.. Rei-ay 350, radio squelch relay, closesA ak ground connection to relay 360, which energizes the radio transmitter 330 and also closesl a circuit to. relay 280 which turns on the Radio supervisoryY lamp 283 and the buzzer 227 thus signalling the operator. The. operator connects. the operator telephone. circuit 230 to the radio trunk 237 andf 238. by movingthe ANS Key 229 to the. Radioposition and requests thenumber of the P. A. X subscriber desired by. the mobile sub.- scriber. Having received the. directory number of the desired P. A. X party to be called, the operator turns the ANS Key'22l). to Vl. A. X position and dials the number from the operator position 230 overv the*l lineV 108. and 199 into the line circuit 10:3Y and its associated connector switch 102 located at l?. A. X 100. After the.. P. VA. X subscriber has answered, the` operator momentarily closes the Trunk Key- 26,4; whichI results in the connection of the radio.: trunk 237 and 23S to the P. A. X line 10,56 aud107f. Thereafter the; operator moves. the ANS.Key 229y to normaL-positionand retires to other duties. phone. circuitV the method of release after the. conversation. has been terminated is identical to the one described previously. inl a call from the P; A` Xsubscriberto one of the-mobile station subscribers. ,Y

Whenever a subscriberk at. one ofV the. mobile stations wants to initiate a cal-l to another mobile Station sube scri-ber, the calling` subscriber turns on the radio, transinitier located at the mobile station. which transmits a carrier wave signal to the radio terminal 300 where it is picked upy by the. radio receiver 340. results in o ifaeration` of the;V radio squelch relay. 35.0, asfpreviously described. which is effective to turn on the radiotransmitter 330- and Valso to signal the op&".1.at t}l"-'itv the attendant station 2% by Vmeans of the Radio supervisory lantev 2&3 and.r thefbuzzer 227. The operatorr rcSPOudS, by operating the ANS Key223`to the Radio P OSOH which by means of its contacts 221- completesv a circuit for relay 259 which thereafter closes its lock circuit by means of contacts 262. Operation of thereljay 26,0 also opens the buzzer circuit by means: Ot the contacts 263.- Y

ContactsV 261 closeA and establish a lotlsillg'v circuit for relay 3691 which in turn tucks the,operatiug'circuit.of the.- radio transmitter 33t). Operation ofthe-ANS Key to the. Radio position also enables the operatorl to hear thatV the call is nobile-to-inobile subscriber and there- Witlirespcct to.. the; operators, teleoperates. the Monito 4g upon returns the ANS Key toits Normal position. Thereafter# theaspeech signal received` by the rad-io receiver'340 from the calling,` mobile subscriber is passed to the dividing network 310 and into the radio transf mitter 33t) where it modulates said radio transmitter to send out a signal on a, diierent frequency over the airwaves to the called" radioW mobile subscriber. To advise any, calling' 1311 A subscriber.; that thel radio channel' is.: not-v aty Vthis timevayailable toy the operatorT after monitoring and establishing that a` conversation has been inititedj between the` mobileY stations,

.If'SQIfeY`V 2.311 to. the' MonitOrrROSition which causes contacts 232 to close and place a short-A across the lines:V 106. and? 10.?y thereby busying the P. A.l X line. The operator monitors the cali Vby means of a handset connectedto the operator telephone circuit 230 or by means of additional equipment, such as monitorspeaker 201. After the ,call has been terminatedgthe operator operates momenetari'lyf the llVijonitor-RLSl Key 23110, RLSpositon thus releasing'-relay260`I by Vopeningitscircuit atfthe; contacts 23,6atl theI sametime removing,V the shorttfrom the4 P; A. X'line. Thereafter the radio' transmitter Sois? shut, ofand the Radio supervisory lamp 283j's` extinguished:-`

Calls from P. A. X to mobiley radio When the circuit.. isY seized; by. one of thef P.. A. X Y

240, and. 250; make.. contacts 2,12. close andoperate the' buzzer 227 from groundthrough themake contacts 21H2,` through the. buzzer 22.7.th10l1gi1. the.y break contacts 2472V on relay. 2.40, throughtlie. break contacts 253 on relay 260, and through the break contacts V257 on relay' 25,0.. to the battery; and maliecontacts 2,12 close, a. circuit for the P- AL. X supervisory m1119214 Causing it to light up aad thereby notify the. attende tf stuatcttat the attendautsV station 200Vv .of auvincomins The attendantresponds bv Operating t11.e -A1.*I,.S. Key 22u-tothe P- A- X position, Causing; the.k Operaticncf relax.'v 24Q`when contacts 2.2.6

Vclore and Complete, a Circuttroul srcundtc the. battery Y through the aforementioned. relaxt Make Contacts 2.2.3

. overthe make contacts .2111, andV over the make contacts 211 on relay 210 to ground.` Thev break contacts 242 open the buzzer circuit thereby silencingthe buzzer 227'. After the calling subscriber gives a request to the attendant toV call a certain mobile unit, the attendant operatesv the 'contacts 225, over the line1238., and through the lower winding 268 ofthe: repeating-coili265'to ground, TheV purpose of the condenser 271iv is topreserve theraijorementionedD. C. circuit and to1 allfowf voice-currents to be transmitted throughthe repeating-.coil 265. Y

'Relay 26'0 operates when current tiows over the path wk... f

arenaria" extending from battery through the winding of relay 260, through break contacts 251l of relay 250, through the break contacts 236 of the Monitor-RLS Key 231, and through the make contacts 221 of the ANS Key 220 to ground. A locking circuit for relay 260 is established from ground through the make contacts 262 of relay 260, through the break contacts 236 of Monitor-RLS Key 231, through the break contacts 251 of relay 250, and through the winding of relay 260 to battery. Make contacts 261 close and ground the simplex leg of the repeating coil 265 at the point 271, thereby turning on the radio transmitter 330 in the manner following. The radio transmitter energizing relay 360 is operated when current flows over the path extending from battery through the winding of relay 360 to the center tap 307 of the repeating coil 301, through both of the windings 302 and 305 to the other two windings 267 and 269A of the repeating coil 265, through the center tap 271, and through the make contacts 261 of relay 260 to ground. Relay 280 which is connected to the center tap 271 also may be energized over the contacts 261 to ground. Make contacts 281 close and establish a multiple ground to the incomplete circuit of the buzzer 227. Make contacts 282 close and complete a circuit to the Radio supervisory lamp 283 causing it to light up and indicate to the operator that the radio transmitter 330 is energized.

The attendant or the operator calls the required radio mobile unit, for example radio mobile unit 400, by speaking into the telephone connected to the operators telephone circuit 230 and thereby modulating the carrier wave transmitted over the air by the radio transmitter 330. After establishing contact the operator connects the P. A. X line to the radio trunk and transfers control of the transmitter energizing circuit from the operator to the calling subscriber in the manner following. The operator momentarily operates the non-locking Trunk Key 264 which at the contacts 258 provides a path to ground from battery through the winding of the relay 250 causing relay 250 to become energized. Make contacts 252 and 253 close and connect the radio trunks 237 and 23S, respectively, to the P. A. X lines 106 and 107 through the condensers 228 and 229, respectively. The purpose of the aforementioned condensers is to isolate the battery supply connected to the windings 266 and 26S of the repeating coil 265 from the battery supply furnished from the connector switch 101 over the lines 106 and 107. The control transfer operation is accomplished when the operation of relay 250 assumes control of the circuits previously controlled by the operation of relay 260 which is de-energized when the contacts 251 of relay 250 are opened. De-energization of the relay 260 opens its own locking circuit at its contacts 262, opens the path to ground or" the transmitter energizing relay 360 at the contacts 261 and re-closes the contacts 263 of the buzzercircuit. Uninterrupted operation of the transmitter energizing relay 360 is insured by simultaneously providing an alternate path to ground when the relay 250 closes the make contacts 255. The buzzer circuit is held open when break contacts 257 open another portion of the buzzer circuit. Operation of relay 250 further closes the contacts 256 in its locking circuit which Ycircuit includes the closed contacts 211 of the operated relay 210. x Since relay 210 is under the control of the calling P. A. X subscriber as hereinafter to be explained, the operation of the relay 250 is therefore also controlled by that subscriber. The attendant, after hearing both parties conversing, returns the ANS Key 220 to normal and retires to other duties.

RELEASING The automatic disconnect feature of present invention, eiected only by a P. A. X subscriber, requires that all of the connectors used in conjunction with the P. A. X

6 equipment be of the type designated as vEither party release with normals of attendants station line reversed. When the P. A. X subscriber originally called the attendants station 200 and the connector 101 switched through, the battery polarity on the attendant station line reversed and the relay 210 operated. Current of the opposite polarity, that is, the current flowing from the line equipment when the connector is released, does not alect relay 210 because rectifier 208 prevents the current from owing in this opposite direction through the relay. Thus when the P. A. X subscriber terminates the call by replacing his handset the connector 101 releases relay 210. Relay 210 restores and opens the make contacts 211 which break the locking circuits to relays 240 and 250; make contacts 212 open the circuit to the buzzer 227; and make contacts 213 open the cir`- cuit to the P. A. X supervisory lamp 214 causing it to extinguish. Relay 250 restores and through its contacts performs the following operations: break contacts 251 close an incomplete circuit'to relay 260; the 'make contacts 252 and 253 open up and disconnect the P. A. X lines 106 and 107 from the radio trunks 237 and 23S, respectively; the make contacts 255 remove ground from the simplex leg of the repeating coil 265 causing relay 360 to restore thus shutting offv the radio transmitter 330; and make contacts 256 open a locking circuit at one point to relay 250. Relay 280 is also restored when the make contacts 255 open up. Relay 240 restores and opens its lock circuit at one point when contacts 241 open up. Break contacts 242 close and prepare the buzzer circuit for the next incoming call. Relay 280 restores and through its make contacts 282 opens the circuit to the Radio supervisory lamp 283 causing it to extinguish.

Calls from mobile radio to P. A. X

When a mobile unit, for example 400, calls the attendant at the attendant station 200, ground is applied to the simplex leg of the trunk at the point 271 of the repeating coil 265 when the receiver squelch relay 350 operates and closes its make contacts 351. As a result, current iiows from ground through the make contacts 351 of relay 350 to the center tap 307 of the repeating coil 301, through both windings 302 and 305, through both windings 267 and 269 of the repeating coil 265, out through the center tap 271, and through the winding on relay 280 to battery. Relay. 280 operates causing the make contacts 281 to close a circuit to the buzzer 227 from ground through the make contacts 281 through the buzzer 227, through the break contacts 242 on relay 240, through the break contacts 263 on relay 260, and through the break contacts 257 on relay 250 to battery. The make contacts 351 also complete an operating circuit to relay 360 which in turn is eective to energize the radio transmitter 330 when the make contacts 361 close. YContacts 282 close a circuit to the Radio supervisory lamp 283 causing it to light to thereby signal the attendant. Hence the attendant is alerted both visually and audibly of an incoming call. The attendant responds by operating the ANS Key 220 to the Radio position. This results in the energization of relay 260 when the circuit is closed from ground' through the make contacts 221 on the ANS Key 220,`through the break contacts 236 of the Monitor-RLS Key 231, through the break contacts 251 on relay 250, and through the winding of relay 260 to battery. Contacts 222 and 225 connect the attendants telephone at the operators telephone circuit 230 to the radio trunk 237 and 238 through the lines 231 and 232', respectively. Make contacts 261 on the relay 260 close and connect ground to the simplex leg of therepeating coil 265 thereby establishing a lock circuit for relay 360 which in turn continues to keep the radio transmitter 330 operating. The radio transmitter 330 operating circuit is locked so that when the radio receiver 340 is no longer receiving a carrier wave signal from the calling mobile-station as arenile of; which, the radio ssuclch relay 35.0.v is..-'restorcd and. around contactsSLa new-sourced.grodadicooacctlo. rable. at: the .malto contactclcl oh. relay 2.6% A; lockhg. circuit.- isestahllshcdfor; rclayZ. whchits contacts 252. close-Y .rcakcontacts 2.6350111111. thc; circhi! tothe hllcr 2.251- thercbyslchcina itl. The; attendantafter aclshowl.:

edsingthe call.;4 is; requested; to calll a suhScrher-oo. the

Pt. A.. .X line.- The-aattendantthch.operates, thc ANS; Key 2.2.0. to tho. P.. A; Xnocltlon; which rcsdlts in. thcchstaizatiion of' relay/1 2.4.0 and. oonncctioaof thc operatorie telephone circuit to,l the lines 10.6; and; 10.7,. Thereafter when the operator'dials thegdesired P. A,4 X subseriberV number.. impulsos. are; Seht fromA the.Y dial, across. the; con.-

Vmeetinglirtless231=f and, 23,21 through` the makecontats 22,3 and: 22A, and over. thelines 106 and 6575 .10;8;and

102, andltctheline: circuit- 1.63; and.; connector Switch 10.2, in the; A. X 115.0;.1 Relaylltoperates;when,the malte contacts 22.6. ont the'ANS-1Kcy,^ 2.29.: close. Themalga con; tacts 241i establislrav lock circuitforrcla2r1dthe break contacts; 2.421 openthc buzzer;circuit.l

When thercalh isV answered, the connector in; use; will switch throughtandfurnish. reverse; battery tothe. lines 111% and: 109,'causing relay` 210.1' to become energized. Relay 210 operates; andV through its makeY contacts 2,13 lightstherP. A. X supervisory/slamp, 214.. MakeV contacts 211. close and. keep. the relay- 240: operated; when the ANS Key 22). is restored; to normal. The, attendantby momentarily. operating the TrunlcKey 2.6.4, .energizes relay n 250. The attendant' then. restoresY the ANS Keyf-ZZtlfto Thek releasing operation is accomplished in a manner similar to that described for R A. X to mobile operation.

Mobz'e to mobile operation When mobile unit, for example 40?, calls another mobile unit, for example 402, ground is placed on the simplex leg of the .trunk Zfland ZVSSjWhen radio squelch relay 350 operates upon the receipt ofia carrier wave signal from a transmitter locatedy at the calling radio mobile unit and closes its malte contacts 351'. rlfhe Radio supervisory lampr l283 lights'up as a result. of the operation` of relay 28d andits make contacts 232. The malte contacts llfcllose a circuit to the buzzer* 22j` cau ing it. to operate aodstuohioh, tho attendant- .By opcro .oh cf the ANS Kcy 220 to thc. Radio Position thc oncrdtorc telephone olrcoitz will. hc cdoocctcd across. thc. radio trunk and the attendant will bear the'mobile unit 4.110 calling another mohiljc doit. 4l2 The operator thch. coctates the' Monitor-RLS Key 231 to the Monitor position causing the P. A. X line to become busy to any incoming P. A. Xcalls. This. is accomplished when the make coritacts 232 on the Monitor-RLS Key 251 close and place a. shortacross the lines M6 and 107. Operation of the ANSKcyZZtl to. Radio position closesthc., mclcccotttactd 22.1 which causo. relay 2.61? to'oocratc AS. c result., ground ls'cloccd on the similcx lcs of thc radio trdoh 2.3.4. cdd

285. This ground completes an operating circuit to the Y yradio transmitter relay Stl'which in turn locks the transto monitora call by means of*` the handsetlocated at the y operators telephone circuit 239er the loudspeaker 201.

Releasing when the mobile. unicatt@ and m2A 4sich all." the attendant orcrfatcs thc McoltorfRLSKcy 231 to thc Release position., thosrclccsihs rclcyit-ttl whchthc.- hfcclc contacts. Zdlopchup.- Thcdivhch hcll/lchitclidLSt Kcy 231:. is. returnedto. nor-mal, the. make.- contacts 232 open 'up and remove thejshort from, the .P. A. X line. 06. and 107. Relay. 260 restores and through. its make. contacts .2,61

' removes theground from thesiiriplelx lieg of the repeating coil 266:5 which, is` instrumentalinl. releasingk relay 56D. and. in consequentlyy shutting oft the radio. transmitter 330. This rein(3x/,alfof'groundl alsofcausesrelay 2.80. to

release, which results in the. extinguishing` of Vthe Radio supervisory lamplrwlhen themake contacts 22openup. While. there has beendescribed what isat presentl conf ,sidered to bathe preferred embodiment of the invention,

ter to said attendant station, a iii-st switching .mear/iis, YaV

first. operation of scid. dict; switching mcchs cohhcctihs Said operators. telephone circuit. tor scid h'hc, a, LSecond operation. of.. Said-.first switching means.' cocrslzlhssc'd radio traasmittcr and cohhcctihg. Said. cocrctor'hf tlnhoac circuit.v to Said' radio trohls c Sccohd. SwitchingV mcchsfor. contacting. Said. llhc to scid .tedio ttchlc cdd d only id. fctoohsc totclccsc of, Said: liuc ly WSaid. calling. Subscribet- Stctioh for independently tid shitoltaacohclyf Sccodcctios caidflihc. fromccid radio truck. and. do: crgizihe scid trahsmittcr- 2- 1.11-4 c. radio tclcohorlccyctcm. c tclcphodc. @Xchahac having c plurality-ot sohscfihcr Stations.. cohhcctcd there to, a radio. transmitter and an attendant station com oficios opctctorfstcldphohc circuit, c; lino.. for'coh.- n cotihs Said crchchseto Said' cttchdcht Station., mcchS' in said exchange controlled acal/ling oney of said sub.- scrilger.V stationstfor connecting to and seizing said line, a radio. truth-tdt coohcctihgl. Said radio; trchshtittcr 'to said attendant station, a lirst switching means, a rst operation of scid, first' switching Inc-cot cohhcctihs Said operators tclcphohc circuit to Shidllhe c Sccohd'opctation of said first f svt/itching means energizing said radio transrnitteijA and conneeting-A saidoperators telephone circuit toi saidradio trunk/a control relay, and asecond switching', means, operation o fg. said second switching means connecting Said. lloc tocaid radio trhhlc and; tract.- ferrillg QOBIIQL Qf said transmitter from said first switching means toV said control relay, said controlrelay operated responsiveto thereleaseof said .line by said callingsubscriber. to independentlycle-energized said transmittel?.

3` Irl.- a radio tolcplioney Systcm` as claimed ih claim, 2, said control relay operated responsive to the release ofk said line byf s aid calling subscriberl to independently disconnect.;said'linerfrom. saidradio truolci Y 4. Ina radio telcnhonesystom, a telephone cxchahec haring a plurality of Subscriber Stations connected.y thctcttl.. a radio trai.lsrnitt/e-t',V and anattendant station'eornprising arrA operatoria telephone circuit, a line for vc011- necting said exchange to. said attendant station, means in said. exchange controlled by a Galliney ontl of Said' subscriber stations for connecting to and seizing said line, a control relay operated responsiye'to seizure of said line by said calling subscriber station, a signaling circuit including signaling means, saidfsignaling circuit conV ttollcd hy Said cohtrol tclcy. to oocrctc Said Sichelihg station,.- a ilrstswitehing'means, a irst operation of-said first switching means connecting said operators telephone circuit to said line and opening said signaling circuit, a second operation of said iirst switching means energizing said radio transmitter and connecting said operators telephone circuit to said radio trunk, and a second switching means, operation of said second switching means connecting said line to said radio trunk and transferring control of said transmitter from said first switching means to said control' relay and transferring the said connection of said line and said radio trunk from said second switching means to said control relay, said control relay operated in response to the release of said line by said calling subscriber station to independently and simultaneously de-energize said transmitter, disconnect said line from said radio trunk and prepare said signaling circuit for further incoming calls.

5. In a radio telephone system, a telephone exchange having a plurality of subscriber stations connected thereto, a radio transmitter, and an attendant station comprising a line for connecting said exchange to said attendant station, means in said exchange controlled by a calling one of said subscriber stations for connecting to and seizing said line, a control relay energized responsive to seizure of said line by said calling subscriber station, and de-energized responsive to the release of said line by said calling subscriber station, a first switching means, a iirst transmitter relay for controlling the energizing of said transmitter, said iirst transmitter relay operated responsive to the operation of said rst switching means to energize said transmitter, a second switching means, and a second transmitter relay for controlling the energizing of said transmitter, said second transmitter relay energized responsive to the operation of said second switching means to transfer control of said transmitter to said second transmitter relay, said second transmitter relay de-energized responsive to the de-energizing of said control relay to thereby de-energize said transmitter.

6. A radio telephone system comprising a private automatic exchange having a plurality of subscriber stations connected thereto, a plurality of mobile radio subscriber stations, each of said mobile stations comprising a radio transmitter and receiver, said mobile transmitters transmitting over a rst channel, and an attendant station comprising a radio transmitter and receiver, said attendant transmitter transmitting over a second channel, an operators telephone circuit, a line connecting said automatic exchange to said attendant station, means in said exchange controlled by any one of said exchange subscriber stations for connecting to and seizing said line, a radio trunk connecting said attendant radio transmitter and receiver to said attendant station, a control relay energized responsive to seizure of said line, a signaling circuit including signaling means, said signaling circuit completed by the operation of said control relay to operate said signaling means, a rst transmitter control circuit including a rst transmitter relay, said control circuit partially completed by the operation of said control relay, a iirst switching means, a first operation of said rst switching means connecting said operators telephone circuit to said line and opening said signaling circuit, a second transmitter control circuit including a second transmitter relay, a second operation of said rst switching means disconnecting said operators telephone circuit from said line and connecting it to said radio trunk and operating said second transmitter relay, operation of said second transmitter relay completing said second transmitter control circuit to energize said attendant transmitter, said operator thereby enabled to communicate with said mobile subscribers over said second channel, and a second switching means, operation or" said second switching means completing said iirst transmitter control circuit to thereby operate said first transmitter relay, operation of said rst transmitter relay transferring control of the energization of said attendant transmitter from said second transmitter control circuit to said first transmitter control circuit, operation of said first transmitter relay further connecting said line to said radio trunk, release of said line by said calling exchange subscriber station de-energizing said control relay to thereby open said first transmitter control circuit thereby simultaneously and independently de-energizing said attendant transmitter and disconnecting said line from said radio trunk.

7. A radio telephone system as claimed in claim 6, said attendant station including a third transmitter relay operated responsive to signals received from any of said mobile radio subscriber stations by said attendant receiver over said first channel, said third transmitter relay operative to complete said signaling circuit and energize said attendant transmitter.

8. In a radio telephone system as claimed in claim 7, an impulse generating dial connected to said operators telephone circuit, a third operation of said first switching means disconnecting said operators telephone circuit from said radio trunk and re-connecting it to said line, and means operated in response to receipt of impulses corresponding to the dialed digits for connecting said line to a desired private automatic exchange susbcriber station.

9. A radio telephone system as claimed in claim 7, in which said signals received from any of said mobile radio subscriber stations' by said attendant receiver over said first channel are re-transmitted by said attendant transmitter over said second channel to said other mobile radio subscriber stations.

l0. A radio telephone system as claimed in claim 9, said attendant station including a third switching means, operation of said third switching means effective to busy said line connecting said automatic exchange to said attendant station to thereby apprise said exchange subscriber stations that said attendant radio transmitter and receiver are unavailable for use.

References Cited in the file of this patent UNITED STATES PATENTS 1,472,987 Murphy Nov. 6, 1923 1,504,204 Andrick Aug. 12, 1924 2,523,914 Molnar Sept. 26, 1950 2,575,782 Bartelink Nov. 20, 1951 

